Substrate with photocatalytic coating

The invention relates to glass-based substrates, ceramic or glass, more particularly of glass, especially transparent, which is provides with coatings photocatalytic properties, in order to manufacture windows of various applications, such as utilitarian glazing, glazing vehicles or buildings.

Increasingly, attempts to functionalize glazing by depositing their surface thin films intended to give them a possession particular depending on the application. Thus, there exist layers with an function optical, such as so-called anti-glare layers composed of a stack of layers alternately high and low refractive indices. For function anti-static, or heating the antifreeze type, there may also be provided electrically conductive thin film, for example based on metal or doped metal oxide. For thermal function, low-emissivity sunscreen for example, we can turn to the thin layers of metal the silver type or based on nitride or metal oxide. For a effect "Rain" can be provided of hydrophobic layers, for example based on fluorinated organosilane ...

However, there still exists a need for a substrate, particularly a windows that could be called "anti-fouling", that is to say to the permanence over time of the appearance and surface properties, and possible in particular to render cleaning and / or improve the visibility, managing to eliminate the progressively accumulating dirt progressively to the substrate surface, including the original soil organic as fingerprints or volatile organic products in the atmosphere, or even soiling the mist like.

We know that there are certain semiconductor materials based metal oxide, which are capable, under the effect of a radiation length proper wavelength, to initiate radical reactions which cause the oxidation of Organic products: generally speaking materials "photocatalytic" or "photo-reactive".

The invention then aims the development of photocatalytic coatings on the substrate, which present a "antisoiling" effect marked vis-a-vis the substrate and that can be manufactured industrially.

The invention relates to a glass-based substrate, ceramic or glass ceramic, especially glass and transparent, provided on at least a portion at least one of its faces with a photocatalytic property in coating comprising titanium oxide at least partially crystallized. The oxide titanium is crystallized preferably "in situ", during the formation of the coating on the substrate.

The titanium oxide is in fact part of the semiconductor which, under the action of light in the visible or ultraviolet range, degrade organic products are deposited on their surface. Choose titanium oxide to produce a glazed effect "anti-fouling" is particularly indicated, and especially as this oxide has good resistance mechanical and chemical: long to be effective, it is obviously important that the coating maintains its integrity, even though it is directly exposed to numerous attacks, especially during assembly the glazing on site (building) or on production line (vehicle), which involves repeated handling by gripping means mechanical or pneumatic, and also once the glazing in place, with abrasion risk (wipers, abrasive cloth) and contact with aggressive chemicals (atmospheric pollutants like SO₂, product maintenance ...).

The choice was made, in addition, on a titanium oxide which is at least partially crystallized because it has been shown that it was much more performance in terms of photocatalytic property of titanium oxide amorphous. Preferably, it is crystallized in anatase form, rutile form or in the form of a mixture of anatase and rutile, with a rate of crystallization of at least 25%, especially about 30 to 80%, especially near the surface (the property being rather a surface property). (We comprises crystallization rate the amount by weight of TiO₂ crystallized based on the total amount by weight of TiO₂ in the coating).

It was also observed, especially in the case of crystallization in the anatase form, the crystal orientation of TiO₂ increasing the substrate had an influence on the photocatalytic performance oxide: there is a preferred orientation (1,1,0) clearly favors photocatalysis.

Advantageously, the manufacture of the coating is made so as to that the crystallized titanium oxide which it contains is in the form of "Crystallites", at least near the surface, that is to say of monocrystals, having an average size of between 0.5 and 100 nm, preferably 1 to 50 nm, preferably 10 to 40 nm, more particularly between 20 and 30 nm. It is in fact in this size range that titanium oxide appears to have a best-photo catalytic effect, probably because the crystallites this size develop a large active surface.

As discussed in more detail later, the obtainable coating based on titanium oxide in many ways:<ul><li>by titanium precursor decomposition (pyrolysis techniques: liquid pyrolysis, powder pyrolysis, pyrolysis CVD called value stage (Chemical Vapor Deposition) techniques associated with the sol-gel: dipping or dipping, cell coating, ...),</li><li>by a vacuum technique (reactive sputtering or not).</li></ul>

The coating may also comprise, in addition to titanium oxide crystallized, at least one other type of mineral material, particularly in the form an amorphous or partially crystalline oxide, for example an oxide of silicon (or mixture of oxides), titanium, tin, zirconium or aluminum. This mineral material may also contribute to the effect photocatalytic crystalline titanium oxide, by itself exhibiting a some photocatalytic effect, even weak compared to that of TiO₂crystallized, which is the case with tin oxide or amorphous titanium oxide.

An oxide layer "mixed" thereby combining the titanium oxide least partially crystallized in at least one other oxide may be interesting optically, especially if the other or others oxides are selected index less than that of the TiO₂ : Lowering the index "overall" refractive coating, can be played on the light reflection of substrate provided with the coating, in particular lower this reflection. It's the case if, for example, one chooses a layer of TiO₂/ Al₂O₃Including a mode obtaining is described in EP-0,465,309, or TiO₂/ SiO₂. It is necessary, of course, that the coating contains, however, a content TiO₂ sufficient to maintain a significant photocatalytic activity. We considers thus it is preferable that the coating contains at least 40% by weight, especially at least 50% by weight of TiO₂ related to total weight of oxide (s) in the coating.

One can also choose to overlay coating according to the invention a oleophobic layer and / or hydrophobic grafted permanent or resistant photocatalysis, for example based on the fluorinated organosilane described in US-5,368,892 and US-5,389,427, as well as perfluoroalkylsilane described in the patent application FR-94/08734 of 13 July 1994 published under suméro FR-2,722,493 and corresponding patent European patent application EP-0,692,463, in particular of formula:<st32:che xmlns:st32="http://lighthouseip.com/">CF₃- (CF₂)_not- (CH₂)_m-Six₃</st32:che>wherein n is 0 to 12, m is from 2 to 5 and X is a hydrolyzable group.

To amplify the photocatalytic effect of the titanium oxide coating according to the invention can firstly increase the absorption band of coating, by incorporating other particles to the coating including metal and based on cadmium, tin, tungsten, zinc, cerium, or zirconium.

One can also increase the number of charge carriers by doping the crystal lattice of the titanium oxide by inserting therein at least one of the elements following metal: niobium, tantalum, iron, bismuth, cobalt, nickel, copper, ruthenium, cerium, molybdenum.

This doping may also be done by surface doping only of titanium oxide or the entire coating, surface doping carried out covering at least a portion of the coating of an oxide layer or of metal salts, the metal being selected from iron, copper, ruthenium, cerium, molybdenum, vanadium and bismuth.

Finally, one can amplify the photocatalytic phenomenon by increasing the yield and / or the kinetics of the photocatalytic reactions by covering titanium oxide, or at least part of the coating which incorporates it, with a noble metal as a thin layer of platinum, rhodium, silver, palladium.

Such a catalyst, for example deposited by a vacuum technique, makes it possible to increase the number and / or the lifetime of entities radical created by the titanium oxide, and so promote the reactions in chain leading to the degradation of organic products.

So entirely surprisingly, the coating exhibits in fact not not one property but two, as soon as it is exposed to appropriate radiation as in the visible and / or ultraviolet radiation, such as radiation Sun: by the presence of photocatalytic titanium oxide, as already seen, promotes the gradual disappearance, as and when they are accumulating, dirty marks of organic origin, their degradation by causing a radical oxidation process. Mineral stains are they not degraded by this process: they therefore remain on the surface, and, apart some crystallization, they are in part easily removed since have no reason to adhere to the surface, organic agents tights being degraded by photocatalysis.

But the coating of the invention, is permanently self-cleaning, also preferably has an outer surface to character hydrophilic and / or oleophilic pronounced, which results in three very advantageous effects:<ul><li>hydrophilicity allows perfect wetting of water that can is deposited on the coating. When a water condensation phenomenon occurs, instead of a deposit of water droplets in the form of mist hampers visibility, there was actually a thin continuous film of water that forms the coating surface and is entirely transparent. This "anti-fog" effect is in particular demonstrated by the measurement of a contact angle to water lower 5 ° after exposure to light, and, </li><li>after water runoff, including rain on a surface not treated with a photocatalytic layer, many drops of rainwater remain attached on the surface and leave, once evaporated, traces unsightly and annoying, mainly of mineral origin. In fact, a surface exposed to the ambient air is rapidly covered by a layer of dirt limiting its water wetting. These soils are added other dirt, including mineral (crystallization, ...) provided by the atmosphere in which bathes the glass. In the case of a surface photoreactive, these inorganic dirty marks are not directly degraded by photocatalysis. In fact, they are very largely eliminated through hydrophilic nature induced photocatalytic activity. this character hydrophilic causes indeed a perfect spreading raindrops. The Evaporation traces are no longer present. In addition, other mineral soiling present on the surface are washed, or redissolved in the case of crystallization, the water film and therefore largely evacuated. This gives a "mineral antisoiling" effect induced in particular by rain,</li><li>together with a hydrophilic nature, the coating can also exhibit oleophilicity, allowing the "wetting" dirt organic which, as for water, then tend to be deposited on the coating as a continuous film less visible as "spots" well located. Thus, a "organic antisoiling" effect that occurs in two times: once it is deposited on the coating, the stain is already inconspicuous. Then it gradually disappears by radical degradation initiated by photocatalysis.</li></ul>

The coating can be chosen more or less smooth surface. A certain roughness may indeed be advantageous:<ul><li>it allows to develop active photocatalytic surface area more large and therefore it induces a greater photocatalytic activity,</li><li>it has a direct influence on the wetting. The roughness in fact enhances wetting properties. A smooth hydrophilic surface will be even more hydrophilic once roughened. One understands by "roughness" here also although the surface roughness and the roughness induced by a porosity of the layer in at least a part of its thickness.</li></ul>

The above effects will be more marked when the coating is porous and rough, resulting in a super-hydrophilic effect of photo-reactive surfaces rough. However, too pronounced a roughness may be detrimental in promoting the incrustation of dirt accumulation and / or by show an unacceptable level optically blurring.

It has thus proved advantageous to adapt the mode of deposit coatings based on TiO₂ so that they present a roughness from about 2 to 20 nm, preferably 5 to 15 nm, this roughness being evaluated by atomic force microscopy by measurement of the value of the deviation quadratic medium (the "Root Mean Square or RMS in English) on a 1 square micrometer. With such roughnesses, the coatings exhibit a hydrophilic nature resulting in a contact angle water may be less than 1 °. It was also found that it was advantageous to promote a certain porosity in the coating thickness. Thus, if the coating consists only of TiO₂, It preferably a porosity of from 65 to 99%, especially 70 to 90%, the porosity being defined here indirectly by the percentage of the theoretical density TiO₂Which is about 3.8. To promote a porosity means consists, for example, depositing the coating by a technique of the sol-gel type, involving the decomposition of organometallic type of materials we can then be introduced into the solution, the addition or the precursor (s) organometallic (s), an organic polymer of polyethylene glycol PEG: in hardening by heating layer burning PEG, which produces this or amplifies a certain porosity in the thickness of the layer.

The thickness of the coating according to the invention is variable, it is preferably between 5 nm and 1 micron, particularly between 5 and 100 nm, especially between 10 and 80 nm, or between 20 and 50 nm. In fact, the choice of the thickness can depend on various parameters, in particular the intended application of the substrate of the glazing type or alternatively the size of crystallite TiO₂ in the coating or the presence of strong alkali in proportion in the substrate.

Between the substrate and the coating according to the invention can have a or more thin layers in different or complementary function of that of the coating. This may be, in particular, layers with an anti-static function, thermal, optical, or promoting the crystalline growth of TiO₂anatase or rutile form or of layers forming a barrier to the migration of certain elements from the substrate, in particular forming a barrier to alkali metals and very particularly to sodium ions when the substrate is glass.

One can also envisage a stack of layers "anti-glare" alternating thin layers with high and low indices, the coating according the invention constituting the final layer of the stack. In this case, it is preferred that the coating is of relatively low refractive index high, which is the case when it consists of a mixed oxide of titanium and silicon.

The layer with an anti-static and or thermal function (heating in the providing it with current leads, low-emissive, anti-solar, ...) can especially be chosen based on a metal-type conductive material such as silver, or metal oxide doped indium oxide as doped with tin ITO, tin oxide doped with fluorine-type halogen SnO₂: F or with antimony SnO₂: Sb or zinc oxide doped with indium ZnO: In, with fluorine ZnO: F, with aluminum ZnO: Al or with tin ZnO: Sn. He can too be of metal oxides substoichiometric in oxygen, such as SnO_2-x or ZnO_2x x &lt;2.

Anti-static fontion layer preferably has a resistance value square from 20 to 1000 ohms / square. Provision can be brought to the bring current to polarize (supply voltages for example of 5 to 100V). This controlled polarization makes particular fight against the order of the size of dust deposits millimeter likely deposit on the coating, in particular dry dust which adheres by electrostatic effect: by suddenly reversing the polarization of layer, "eject" the dust.

The thin layer with an optical function can be chosen to reduce the light reflection and / or make it more neutral color in reflection substrate. It has in this case, preferably, a refractive index intermediate between that of the coating and that of the substrate and a thickness appropriate optics, and can be made of an oxide or a mixture oxide type oxide of aluminum Al₂O₃, Tin oxide SnO₂, oxide indium In₂O₃Oxycarbide or silicon oxynitride. For a maximum attenuation of the color in reflection, it is preferable that this thin layer has a refractive index close to the square root of product of the squares of refractive indexes of the two materials the frame, that is to say the substrate and the coating according to the invention. Meanwhile, it is advantageous to choose its optical thickness (that is to say the product of its geometric thickness and of its refractive index) neighbor lambda / 4, lambda being approximately the average wavelength in the visible, in particular approximately 500 to 550 nm.

The thin layer to alkali-barrier function can be especially chosen based on silicon oxide, nitride, oxynitride or oxycarbide silicon, aluminum oxide containing fluorine Al₂O₃F, or nitride aluminum. In fact, it proved useful when the substrate is glass, because migration of sodium ions into the coating according to the invention may, in certain conditions, detrimentally affect the photocatalytic properties.

The nature of the substrate or of the sublayer furthermore has an interest Extra: it can promote the crystallization of the layer photocatalytic that is deposited, in particular in the case of CVD deposition.

Thus, during CVD deposition of TiO₂, A sub-layer of SnO₂F crystallized promotes the growth of TiO₂ as predominantly rutile, particularly of the order of deposition temperatures of 400 ° to 500 ° C, then that the surface of a soda-lime glass or oxycarbide underlayer silicon rather induces an anatase growth, in particular for deposition temperatures of the order of 400 ° to 600 ° C.

All these optional thin layers can, in known manner, be deposited by vacuum techniques of the sputtering type or by other techniques of the thermal decomposition type such as pyrolysis into solid, liquid or gaseous. Each of the abovementioned layers may hold several functions, but they can also overlay.

The invention also relates to glazing "antifouling" (Organic and / or mineral soiling) and / or "anti-fogging", whether monolithic, multiple insulating double glazing or laminated type and incorporates the coated substrates described above.

The invention is therefore the production of glass products, ceramics, vitro ceramic, especially the manufacture of glass "self-cleaning ". These can advantageously be building glazing, as double glazing (it is then possible to arrange the coating "side outside "and / or" inner side ", that is to say on face 1 and / or on face 4). This proves especially advantageous for inaccessible glazing cleaning and / or which need to be cleaned very frequently, such as glazing roof, airport glazing ... It may also include windows for vehicles where maintaining visibility is an essential criterion security. This coating can thus be arranged on the windshield, side or car rear windows, especially on the face of the windows turned to inside the passenger compartment. This coating can then prevent fogging, and / or remove traces of dirt on the type of fingerprints, nicotine or organic material of the volatile plasticizer-type released by the plastic dressing inside the passenger compartment, in particular that of the dashboard (release known sometimes under the term of "fogging"). Other vehicles such as airplanes or trains can also find interest in using glazing fitted the coating of the invention.

Many other applications are possible, especially for glasses aquarium, shop windows, greenhouses, conservatories, glass used in the interior furniture or street furniture but also mirrors, TV screens, the field of eyeglasses or any architectural material type facade material, siding, roofing such as tiles, ...

The invention thus allows to functionalize these known products, their conferring anti-ultraviolet, anti-fouling, bactericidal, anti-reflective, anti-static, anti-microorganism, ...

Another interesting application of the coating according to the invention is to associate it with a controlled variable absorption glazing electrically types: electrochromic glazing, liquid crystal glazing optionally with dichroic dye, glazing particle system suspended, viologen glazing ... All these glasses are generally composed a plurality of transparent substrates between which there are arranged "active" elements, can then be advantageously to arrange the coating on the outer face of at least one of these substrates.

Particularly in the case of an electrochromic glazing, when the latter is in the colored state, its absorption results in a degree of surface heating, which in fact is likely to accelerate the photocatalytic decomposition carbonaceous substances which are deposited on the coating according to the invention. For details on the structure of an electrochromic glazing, reference will advantageously be made to the patent application EP-A-0575207 describes an electrochromic laminated double glazing, the coating according to the invention may preferably be disposed opposite one.

The invention also relates to different processes for obtaining coating according to the invention. We may use a deposition technique the type pyrolysis, particularly interesting because it allows the deposit of continuous coating directly on the float glass ribbon, when uses a glass substrate.

Pyrolysis may be performed in solid phase, from powder (s) precursor (s) of the organo-metallic type (s).

The pyrolysis can be carried out in liquid phase, from a solution comprising an organometallic titanium precursor of the type chelate titanium and / or titanium alkoxide. Such precursors are mixed with at least one other organometallic precursor. For more details on the nature of titanium precursor or on the deposition conditions, reference should be made by example patents FR-2310977 and EP-0465309.

Pyrolysis can also be effected in vapor phase, which technique is also referred to as CVD (Chemical Vapor Deposition) from at least one titanium precursor of the halide such as TiCl₄ or alkoxide titanium tetraisopropoxide type Ti, Ti (OiPr)₄. crystallization of the layer can further be controlled by the type of sublayer, as mentioned above.

Can also deposit the coating by other techniques, especially by the techniques associated with "sol-gel". Different modes of deposit are possible, as the "tempered" also called "dip-coating" or deposition using a cell known as "cell coating". It can also be a deposition mode by "spray coating" or by laminar coating, the latter technique is detailed in patent application WO-94/01598. All these deposition methods typically use a solution comprising at least one organometallic precursor including titanium alkoxide which is decomposed thermally after coating the substrate with the solution on one of its faces or on both sides.

It can be advantageous, moreover, to deposit the coating of any is the deposition technique envisaged, not at once, but by the least two successive steps, which appears to promote the crystallization of titanium oxide over the entire thickness of the coating when selecting a relatively thick.

Similarly, it is advantageous to subject the coating property photocatalytic, after deposition, a heat treatment of the annealing type. A Heat treatment is essential for a technique of sol-gel type or laminar coating to decompose (s) precursor (s) organometallic (s) oxide, once the coating of the substrate and improve performed the abrasion resistance, which is not the case when using a technical pyrolysis where the precursor decomposes as soon as it is at the contacting the substrate. In the first case as in the second, however, a post-deposition heat treatment, once the TiO₂ formed, improves its rate crystallization. The chosen treatment temperature can also enable to better control the rate of crystallization and the crystalline nature, anatase and / or rutile, of the oxide.

However, in the case of a soda lime glass substrate, of multiple and extended to annealing can promote mitigation the photocatalytic activity because of excessive migration of alkali substrate towards the photoreactive layer. The use of a barrier layer between the substrate, if it is standard glass, and the coating, or the choice of a adequately composition glass substrate, or the choice of a glass soda-lime whose surface is dealkalized allow to overcome this risk.

Other details and advantageous features of the invention emerge the description below of non-limiting exemplary embodiment, with the following figures:<ul><li><b>figure 1 :</b> a cross section of a glass substrate provided with the coating according to the invention,</li><li><b>Figure 2:</b> a diagram of a deposition technique, sol-gel, so-called "dip" or "dip coating" the coating,</li><li><b>Figure 3:</b> a diagram of a deposition technique called "cell coating"</li><li><b>Figure 4:</b> a diagram of a deposition technique called "spray coating"</li><li><b>Figure 5:</b> a diagram of a deposition technique by laminar coating.</li></ul>

As shown extremely schematically in Figure 1, all the following examples relate to the deposition of a coating 3 says "antifouling "Essentially based on titanium oxide on a substrate 1 transparent.

The substrate 1 is in clear soda-lime-silica 4mm thick and 50 cm long and wide. It goes without saying that the invention is not limited to this specific type glass. The glass can also not be flat, but curved.

Between the coating 3 and substrate 1 is a thin layer Optional 2 or based on silicon oxycarbide SiOC to constitute a diffusion barrier to alkali and / or a layer which attenuates light reflection, or tin oxide doped with fluorine SnO₂F for to form an anti-static layer and / or low-emissive effect even basémissif slightly accentuated, and / or attenuating the color in particular in reflection.

<u>EXAMPLES 1 TO 3</u>

Examples 1 to 3 relate to a coating 3 deposited using a technique in the liquid phase pyrolysis. Can be carried out continuously, using a suitable distribution nozzle arranged transversely and above float glass ribbon, to leave the enclosure of the float bath well said. Here, we conducted batchwise, using a nozzle mobile disposed opposite the substrate 1 already cut to specified dimensions, which substrate is first heated in an oven at a temperature of 400 to 650 ° C before marching constant speed past the nozzle projecting a appropriate solution.

EXAMPLE 1

In this example, there is no optional layer 2. The coating 3 is deposited using a solution comprising two organometallic precursors titanium, di-iso-propoxy-di acetylacetonate and titanium tetraoctylene titanium glycolate dissolved in a mixture of two solvents, which are ethyl acetate and isopropanol.

It may be noted that other precursors of the same type are entirely made used also including other titanium chelates of the type titanium acetylacetonate, titanium methylacetoacetate, ethylacetoacetate of titanium or titanium tri-ethanol amine or titanium di-ethanol amine.

Once the substrate 1 has reached the desired temperature in the furnace or especially about 500 ° C, the latter moves past the nozzle projecting room temperature the mixture indicated with the aid of compressed air.

This gives a layer of TiO₂ about 90 nm thick, the thickness can be controlled by the line speed of the substrate 1 in front of the nozzle and / or the temperature of said substrate. The layer is partially crystallized in the anatase form.

This layer has excellent mechanical strength. its resistance to abrasion tests is comparable with that obtained for the glass surface naked.

It is bendable and tempered. It does not present sail: the diffuse light transmission of the coated substrate is less than 0.6% (Measured under illuminant D₆₅ at 560 nm).

EXAMPLE 2

II renews Example 1, but with the interposition between the substrate 1 and coating 3, a layer of SnO 2₂: F of 73 nm thick. this layer is obtained by powder pyrolysis from dibutyltin difluoride DBTF. Can also be obtained in known manner, by liquid phase pyrolysis or steam, as described for example in EP-AO patent application 648 196. vapor that may especially use a mixture of monobutyl tin trichloride and of a fluorinated precursor optionally associated with a oxidant "soft" H-type₂O.

The index of the layer obtained is about 1.9. Its square resistance of approximately 50 ohms.

In Example 1 above, the coated substrate 1, mounted in double glazing so that the coating is on face 1 (with another substrate 1 'not coated but of the same nature and dimensions as the substrate 1 via an air gap of 12 mm) has a value of purity of color in reflection of 26% and a color purity value in transmission of 6.8%.

In this example 2, the color of purity in reflection (in gold) is only 3.6% and is 1.1% in transmission.

Thus, the sub-layer of SnO₂F possible to impart to the substrate anti-static properties due to its electrical conductivity, it also a favorable influence on the colorimetry of the substrate, making it significantly more "neutral" its color, both in transmission and in reflection, coloration caused by the presence of the coating 3 of titanium oxide having a relatively high refractive index. Can polarize in the equipping a suitable power supply, for limiting the deposition of dust of relatively large size of the order of millimeters.

In addition, this sublayer decreases the diffusion of alkali metals in the photocatalytic layer of TiO₂. The photocatalytic activity is improved.

EXAMPLE 3

It renews Example 2, but this time intercalating between the substrate 1 and coating 3, a layer 2 based on silicon oxycarbide with an index of about 1.75 and a thickness of about 50 nm, which layer is obtainable by CVD from a mixture of SiH₄ and ethylene diluted in nitrogen, as described in patent application EP-A-0 518 755. This layer is particularly effective in preventing the tendency of alkali metals (N / A⁺, K⁺) And alkaline earth (Ca⁺⁺) From the substrate 1 to the coating 3 and thus the photocatalytic activity has improved significantly. Having as SnO₂: F, a refractive index intermediate between that of substrate (1.52) and coating 3 (about 2.30 to 2.35.), it allows also reduces the intensity of the coloration of the substrate, both in reflection and in transmission and generally reduce the value of reflection light R_L said substrate.

Examples 4 to 7 relate deposits by CVD.

<u>EXAMPLE 4 7</u>

EXAMPLE 4

This example relates to the CVD deposition of the coating 3 directly the substrate 1 using a standard nozzle such as that shown in Patent Application EP-A-0518755 supra. As precursors, are used either an organometallic or a metal halide. Here is chosen as organometallic titanium tetraisopropoxide, interesting for its great volatility and high operating temperature range, from 300 to 650 ° C. The deposition is carried out in this example at about 425 ° C, the thickness of TiO₂ East 15 nm.

Tetra-ethoxy titanium Ti (O-Et)₄ may also be suitable, as halide include TiCl₄.

EXAMPLE 5

It is carried out similarly to Example 4, except that the layer is deposited 15 nm of TiO₂ not directly on the glass but on a sublayer SiOC 50 nm deposited as in Example 3.

EXAMPLE 6

It is performed as Example 4, except that the thickness of the layer TiO₂ is 65 nm.

EXAMPLE 7

II is carried out as in Example 5, except that the thickness of the layer TiO₂ is 60 nm.

From these examples 4 to 7, it is found that the substrates thus coated exhibit good mechanical resistance to abrasion tests. In particular, not observed delamination of the layer of TiO₂.

EXAMPLE 8

This example uses a technique associated with the sol-gel method using a deposit by "dipping", also called "dip coating", the principle of spring Figure 2: it is immersing the substrate 1 in the liquid solution 4 container (s) precursor (s) suitable (s) of the coating 3, then extracting the substrate 1 at a controlled rate using a motor means 5, the choice of extraction speed to adjust the thickness of solution remaining at the surface of the two faces of the substrate and, in fact, the thickness of coatings deposited, after heat treatment of the latter for both to evaporate the solvent and decompose the precursor into oxide.

the coating 3 a solution comprising 4 is used to deposit either titanium tetrabutoxide Ti (O-Bu)₄ stabilized with diethanol amine DEA in a molar ratio 1: 1 in a solvent like ethanol 0.2 mole of tetrabutoxide per liter of ethanol, or the precursors and the solvent mixture described in Example 1. (Can also be used as another precursor dibutoxy-titanium diethanolamine).

The substrates 1 can contain SiOC sublayers.

After extraction of each of the solutions 4, the substrates 1 are heated 1 hour at 100 ° C then 3 hours at 550 ° C with a rise in gradual temperature.

Is obtained on each side a coating 3, in both cases TiO₂ well crystallized in the anatase form.

EXAMPLE 9

This example uses the technique called "cell coating", the principle is recalled in figure 3. This is to form a narrow cavity delimited by two substantially parallel faces 6, 7 and two seals 8, 9, at least one of these faces 6, 7 consisting of the face of the substrate 1 to be treated. then fills the cavity of the solution 4 of precursor (s) of the coating and is removed solution 4 in a controlled manner, so as to form a meniscus of wetting with October 1 peristaltic pump for example, leaving a film of the solution 4 on the face of the substrate 1 progressively withdrawing the solution.

The cavity 5 is then maintained for at least the time required for a drying. Curing of the film is performed by heat treatment. The advantage of this technique compared to "dip-coating" is particularly which can handle only one of the two faces of the substrate 1, not both systematically, unless you use a masking system.

The substrates 1 comprise thin layers 2 based oxycarbide SiOC silicon.

Example 6 uses respectively the solutions 4 described in Example 8. The same heat treatments are then made to obtain the coating TiO 3₂.

The coating 3 exhibits good mechanical durability.

It appears SEM (scanning electron microscope) an effect field in the form of "grains" of diameter single crystal 30 nm. The roughness of this coating induces wetting properties exalted relative to a non-rough coating.

These same solutions 4 can also be used to deposit coatings by "spray coating", as shown in Figure 4, where one sprayed with the solution 4 as a cloud against the substrate 1 in static, or by laminar flow coating as shown in Figure 5. In the latter case, passing the substrate 1, held by vacuum suction against a support 11 stainless steel and Teflon, over a tank 12 containing the solution, solution in which is partially immersed a slotted cylinder 14 is then moves the entire tank 12 and the cylinder 14 over the entire length of the substrate 1, the mask 13 preventing rapid evaporation of solvent of the solution 4. For more details on this last technique, will advantageously be made to the patent application WO-94 / O1598 above.

Tests were performed on the substrates obtained in Examples previous to characterize the deposited coatings and evaluate their performance "anti-fog" and "anti-fouling".<ul><li><b>Test 1:</b> it is the test of condensation figures. It is to observe consequences of the photocatalysis and coating (rates of hydroxyl groups, porosity, roughness) on the wetting. If the surface is photo-reactive, the carbon micro-pollution settling on the coating are destroyed permanently, and the surface is hydrophilic so antifog. One can also make a quantitative assessment warming suddenly the coated substrate initially cold stored or simply by blowing on the substrate, by measuring if condensation appears and if so, at what time, then measuring the time required the disappearance of the said condensation.</li><li><b>Test 2:</b> it is to evaluate the hydrophilicity and the oleophilicity at the surface of coating 3, in comparison with those of the surface of a bare glass, by the measurement of contact angles of a drop of water and a drop of DOP (dioctyl phthalate) on their surfaces, after having left the substrates for one week to the ambient atmosphere under natural light in the dark and then having submitted 20 minutes to UVA radiation.</li><li><b>Test 3:</b> it consists of depositing on the substrate to evaluate a layer of organosilane and irradiated with UVA in order to degrade by photocatalysis. The organosilane modifying the wetting properties, measurements of water contact angle with the substrate during irradiation indicate the state of degradation of the grafted layer. The rate of disappearance of this layer is related to the photocatalytic activity of the substrate.</li></ul>

The grafted organosilane is a trichlorosilane: octadecyltrichlorosilane (OTS). The grafting is carried out by dipping.

The test apparatus consists of a rotary carousel of around 1 to 6 low pressure UVA lamps. The specimens to be evaluated are placed in the carousel, face to assess the UVA radiation side Depending on their position and the number of lighted lamps, each specimen receives a radiation UVA ranging from 0.5 W / m² 50 W / m². For Examples 1, 2, 3, 8 and 9, the irradiation power is chosen to 1.8 W / m²And for Examples 4 to 7 0.6 W / m².

The time between each measurement of the contact angle varies between 20 min and 3 h, depending on the photocatalytic activity of the test specimen under consideration. Measures are carried out using a goniometer.

Before irradiation, the lenses have an angle of about 100 °. We considered that the layer is destroyed after irradiation when the angle is less than 20 °.

Each test specimen tested is characterized by the average speed disappearance of the layer, given in nanometers per hour, that is to say the thickness of the organosilane layer deposited divided by the duration radiation to reach a lower final level at 20 ° (time disappearance of the organosilane layer).

All previous examples pass the test 1, that is to say when blowing out the substrates coated with the coating, they remain perfectly transparent, as if deposited a layer of condensation well visible on uncoated substrates.

The examples were tested 2: the coated substrates, after exposure UVA radiation, exhibit a water contact angle and to the DOP at most 5 °. In contrast, a bare glass under the same conditions has a water contact angle of 40 ° and a contact angle with DOP of 20 °.

The table below summarizes the results of the coated substrates according the previous examples to test 3.<tables><table><tgroup cols="2"><tbody><row><entry align="center"><b>substratum</b></entry><entry align="center"><b>Test 3 berth to 1.8 W / m² UVA (in nm / h)</b></entry></row><row><entry align="left">Example 1 (TiO₂ on bare glass)</entry><entry align="center">0.03</entry></row><row><entry align="left">Example 2 (TiO₂ on SnO₂F)</entry><entry align="center">0.1</entry></row><row><entry align="left">Example 3 (TiO₂ on SiOC)</entry><entry align="center">0.2</entry></row><row><entry align="left">Example 8 (TiO₂ on 50 nm SiOC)</entry><entry align="center">5</entry></row><row><entry align="left">Example 9 (TiO₂ on 50 nm SiOC)</entry><entry align="center">5</entry></row><row><entry align="left">bare glass</entry><entry align="center">0</entry></row></tbody></tgroup></table></tables><tables><table><tgroup cols="2"><tbody><row><entry align="center"><b>Substrate (CVD)</b></entry><entry align="center"><b>Test 3 berth to 0.6 W / m² UVA (in nm / h)</b></entry></row><row><entry align="left">Example 4 (TiO₂ on bare glass)</entry><entry align="center">&lt;0.05 nm / h</entry></row><row><entry align="left">Example 5 (TiO₂ on SiOC)</entry><entry align="center">4</entry></row><row><entry align="left">Example 6 (TiO₂ on bare glass)</entry><entry align="center">9</entry></row><row><entry align="left">Example 7 (TiO₂ on SiOC)</entry><entry align="center">19.5</entry></row></tbody></tgroup></table></tables>

The table, we can see that the presence of sub-layers, including SiOC, promotes the photocatalytic activity of the coating containing TiO₂By its barrier effect to alkali and alkaline earth migratable glass (comparison of Examples 4 and 5 or 6 and 7).

also observed that the thickness of the coating containing TiO₂ play also a role (comparison of Examples 1 and 3): for a thickness of coating TiO₂ greater than the average size of single crystals or "Crystallites", a better photocatalytic effect is obtained.

In fact, it has been observed that it is the coatings of TiO₂ obtained CVD which exhibit the most advanced crystallization, with sizes of crystallites of the order of 20 to 30 nm. We can see that the activity photocatalytic of Example 6 (65 nm of TiO₂) Is significantly greater than that of Example 4 (15 nm of TiO₂ only). It is therefore advantageous to provide a coating thickness of TiO₂ at least twice the average diameter of the crystallites which it contains. Alternatively, as is the case of Example 5, it can retain a thin coating thickness in TiO₂ but then choose to use an underlayer of nature and thickness appropriate to best promote crystal growth of TiO₂ from the "First" layer of crystallites

It has been observed that the crystallization of TiO₂ was a little less thrust for coatings deposited by a technique other than CVD. Here again, However, everything is a matter of compromise: a less advanced crystallization and photocatalytic activity a priori may be lower "Compensated" by the use of a less expensive deposition process or less complex, for example. In addition, the use of an underlayer appropriate or doping TiO₂ can improve the photocatalytic performance if necessary.

also be ascertained from the comparison of Examples 2 and 3 that the nature of sublayer influences the mode of crystallization and, in fact, the activity photocatalytic coating.